FLAC with wrong but valid 'header' makes decoder misbehave

Description

Summary of the bug: I found a file where libavcodec thinks the file is 8kHz, 3 channel while the file is 44.1kHz and stereo. With ghex I found out this is probably because there is a valid header (CRC checks out) somewhere halfway a block. While this is only one header versus 11 valid ones, libavcodec thinks this one is valid and the rest is garbage.

How to reproduce:

Get flac-file-with-valid-header-in-last-block.flac from upload.ffmpeg.org/incoming

Try 'ffmpeg -i flac-file-with-valid-header-in-last-block.flac test.wav' and see that the resulting file is 8kHz, 3-channel